Three coordinate display system



Oct. 17, 1961 R. coBuRN ETAL THREE cooRDNATE DISPLAY SYSTEM 2Sheets-Sheet 1 Filed Sept. 30, 1953 A TTORNEYS Oct. 17, 1961 R. coBURNErAL THREE COORDINATE DISPLAY SYSTEM 2 Sheets-Sheet 2 Filed Sept. 30,1955 INVENTOA moms/w cosa/mv BY .10H/v DONAHUE ATTORNEYS s ons 19s THREECOORDINAI DISPLAY SYSTEM Richard Coburn, 2018 Catalina Blvd., and JohnDonahue, 244 Catalina Blvd., both of San Diego,`Calif.

Filed sept. 3e, 1953, ser. No. 383,414 5 6 Claims. (Cl. 343-79) 1(Granted under Title 35, U.S. Code (1952), sec. 266) The inventiondescribed herein may be manufactured and used by or for the Governmentof the United States 10 of America lfor governmental purposes withoutthe payment of any royalties thereon or therefor.

This invention relates to a three coordina-te display system and moreparticularly to a system for the three coordinate display of spatialtarget information in orthographic projection on cathode ray tubes.

Many attempts have been made to portray information Vobtained by radarscanning in three dimensions. Most of these systems portray twodimensions in a conventional manner in a plan position indicator,usually the the length of a radial line extending toward the target, or

a vertical strobe'th'rough the target. Read out of the third dimensionalinformation is usually approximate or at best very inaccurate andoftentimes confuses or completely obliterates the information whichwould normally be obtained from the planposition-indicaterf--Senaetimeseease-sother tube is used displayingrange plotted against height. Another system :utilizes the plm positionindicator showing bearing and range on an inner circle and the heightshown on an outer annulus, where the radial distance from the outer'edgeof the inner circle indicates the height 35 of the target. The twodisplays are correlated by means of target bearing, and, where twotargets lie on the same bearing, it is impossible to determine theheight of each individual target. None of these systems portray the'three dimensional information in a forni which presents 40 a clearvisual concept of the spatial arrangement of the objects such as land,air or sea targets with respect to own ship or adjacent land masses andconfigurations. Various forms of synthesized stereoscopic pictures havealso been utilized for displaying three dimensional informationutilizing polarized light or two color pictures with two images suitablyodset and diminished to give a pictorial elect of three dimensions inspace.

Although lmany methods for three dimensional and three coordinatedisplays have been utilized or proposed,

all of these methods have serious limitations in one or more respects.Many of these methods are not adequate i in a quantitative sense, sincethe pictures displayed are not accurate in all three dimensions, andothers which portray accurately all dimensions are not 4adequatequalitatively 55 for interpretation by the operator, since they arepresented in a manner which makes it difficult to conceive the spatialconguration of the targets. Under certain conditions With multipletargets, the presentations of the previous methods result inoverlapping, clutter, confusion, or

ambiguity with respect to the actual location of the targets andfnomeans is known for resolving these ambiguities. Another seriousinadequacy of the previousmethods is the lack of system adaptabilitywith respect to the coordinate input which is acceptable to the systems,flexibility of function and the different electronic systems with whichthe display may be utilized. The information which may be-'fed into adisplay system might consist of cylindrical, spherical, or rectangularcoordinates, and in most of the previousA methods only two of thesethree systems of coordinates are acceptable. In many of the priorsystemsthe information could not be plotted at all `or could not States PatentZ3,005,195 lsatented Oct. 17,1961

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one electronics system and can only be utilized with dilie culty, if atall, with the other electronics systems, such as radar, simulators, andsonar. Many of the renements which can be Iutilized in connection withsome visual displays are not universally fusable with all such displays.Earth curvature corrections, expandable scale, olf-centering, andplotting directly on the scope with a conductive galss overlay foraccurate read out cannot be utilized with many of the previous systems.Each of the prior art systems or methods of display in three coordinatesor three dimensions -is deficient in certain respects.

One preferred embodiment of the present invention as disclosed hereinconsists of a circuit for resolving raw radar data and 'applying it tothe deflection coils and grids of two cathode -ray tubes to produce anelevation view in one tube and a plan view in the other tube,representing the target or targets accurately in the X yand Zcoordinates arid in the X and Y coordinates respectively.

One object of the present inventionis to provide a system and displayfor presenting three coordinate target information in correlated planand elevation views wherein the additional information is presented intrue distortion free coordinates to provide a clear conceptV of three vdimensional structural conguration to the operator.`

Another object of the present invention is to provide an improved methodand apparatus for presenting a `thi-eeYceerdinate-displaykorrcathoderayctnneswvh' ereiniaiirmr" eefn r"coordinates are represented accurately to facilitate read out andtracking. Y

Another object of the present invention is to provide an improveddisplay for a three coordinate target informa-v tion which facilitatesinterpretation and the perception of spatial configuration by acorrelation analogous toI utilized three coordinate input systems, thatis, spherical,

cylindrical, and rectangular, and which may be utilized in conjunctionwith radar, sonar, and various types of simulaters.

A still further object of the present invention is to provide a threecoordinate display which minimizes overlapping, clutter and confusionand wherein ambiguities may be readily resolved without affecting thequalitativeV interpretation of the display. i i Y` Still another objectof the present invention is to provide a system and apparatus for rthedisplay of three dimensional information which may 'be readily modifiedto utilize numerous refinements to facilitate rapid and accurateinterpretation and use of the information such as earth curvaturecorrections, expandable scales, olf-centering, plotting on a conductiveglass overlay on the cathode ray tube, and the use of hooking andlautomatic tracldng techniques commonly used in conjunction with theconventional'plan position indicator type of display.

Still another and further object of the present invention is to providea method and apparatus for resolving and displaying information obtainedin three coordinates.

which may be readily modified or expanded, and providedv with suitableswitches and controls for accepting numerous types of input, anddisplaying the spatial target information in a number of differentmanners utilizing the same basic system and circuitry.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same-- becomes better understood byreference to the followingY 3 detailed description when considered inconnection with the accompanying drawings wherein:

FIG. 1 is a block diagram illustrating one preferred form of thepresent. inventiony applied to a radar system utilizing elevation and.azimuth; antennae.

FIGS. 2 through 6 are a series of correlated views of the; imagespresented on the upper and lower tubes. to showv theu development of aplurality of targets and land masses during- 18,0 degrees of the sweep.

Referring now to thedrawing in detail and particularly to. FIG.. 1wherein one preferred and simplified embodiment of the, presentinvention is; shown in block diagram forum in conjunction with a radar.system utilizing; two antennas, an elevation antenna and an azimuthantenna. Bothl antennas are rotated about a vertical axis at arelatively slow speed usually about 1 to 40 revolutions per minute. Theelevation antenna or the energy beam therefrom .in addition isoscillated about a horizontal axis at a more rapid rate which may be,for instance, approximately. 12 cycles per second or any other desiredspeed which-Will` produce a picture of adequate resolution. v The syncgenerator or timer transmits a synchronizing signal to each of thetransmitters connected.- tothe azimuth and elevation antennas and to thesweep generators fortheV upper and lower cathode ray tubes 11v andl-Z.,

A pair of resolvers 16 and 17 arel suitably connected. mechanically orelectrically to the antennae for synchronous revolution therewith at thesame speed as the rotation. of the antenna about the vertical aX-is.Each, of the resolversl isV connected respectively to itsassociatedsweep generator and amplier, and produces an X and Y Componentor signal corresponding to the relative bearing orpolar angular aspectof the antenna.

A height sweep generator is connected to a tilt potentiometer 1t)mounted on the elevation antenna assemb-ly and which in FIG. l islocated within the box which depicts the elevation antenna assembly. Thepotentiometer; develops a voltage corresponding to` the angle,ofelevationV of the narrow beam of the elevation antenna which is fed tothe-,height sweep generator. The height sweep. generator; develops asawtooth-voltage which is ap;- plied throughthe Z sweep amplifier andthe Z deliection amplifier' to the vertical deflection coil of cathoderay tube` 11.,

The X and Y components or signal voltages developed by one` ofV theresolvers 17 are applied through the X sweepamplier and Y sweepamplifier respectively and thence through the X detlectionamplierand Ydeflection amplilier respectively to the horizontal and verticalcoilsrof the lower cathode ray tube 12, whereas only the X component' orsignal Voltage of the other resolverl 16 is appliedfthroughan X sweepamplifier and X. deiiection amplifier to the horizontal coil of thecathode raytube 11. Suitable gates and clamps` are applied tothe sweepamplifiers and the grids of tubes 11 and 12.

,The video signals received by the lantennae are transrnitted'l throughan elevation receiver and' anl azimuthv receiver` and thence throughvideoy amplifiers to the cath- Oda-ray tubes 11 and 12 respectively,Suitable height markers `,may also be appii-ed through the videoampliiier tf1-the; cathode ray tube 11. A range marker oscillator which;is triggered by a signal from the sync generator activates a pair ofvrange markers Which-supply airintensifying range marker signal to'eachofthe cathode ray; tubes through their respective video amplifiers..

The .pictures displayed by the upper and lower,r cathode rayrtubesf 11and 12 are clearly illustrated'inthe series of FIGS'.-. 2` through 6which show lthe development ofa plurality of lair and sea targets andland massesover a 1'80'5degree sector taken at 45v degree intervals'.`The actua-l picture displayedon the tubes 1'1`and-12 will appear aslight lines and areas formed'by activation-of the phosphorescent'coatingv by the electron beam on thedark face ofthe, tube, butisshownasdark .linesl andsh'aded` areas on a white background'for clarity in thedrawings.

It will be apparent that, during a single complete elevation cycle, lacomplete ltriangular area will be scanned by a plurality of radial lineson the tube 11 while a single line is being scanned repeatedly on thetube 12 as illustrated in FIG. 2. While only nin-e lines have been showncovering the triangulal area on tube 11- for thel sake of clarity-itwill be understood that this area will'be covered in actualY use by alarge number of lines corresponding to the number of discrete signalstransmitted during each eriodv of oscillation of the elevation antenna,and each line will have a plurality of intensified spots such las thoseindicated at 13 at equal intervals produced by the range marker whichcorrespond to the range markingspots 15 onV the lines on tube 12.Actually the plurality of spots at each interval of horizontal rangewill blend into a num-ber of vertical lines.

FIG. 3 illustrates the development of an air target A1 and a land massL1 after 45 degrees rotation of the sweep, the sweep being shown during1 cycle of the elevation antenna and the targets remaining on the screendue to persistence of the intensified spots and areas caused by thevideo signal.

The picture is shown in FIG. 4 with the sweep at 90 degrees from thatshown in FIG. 2, and in this position it isA possible to have someambiguity with two; targets directly in line and at different ranges andelevations. However, this ambiguity could be resolved at once byrotation of the target iield degrees from the position shown. Gradualrotation of the target ield would permit the viewer to see any sectionalelevation view which he desires. While provision for rotation has notbeen shown in the block diagram of FIG. 1, such modification could bereadily applied utilizing conventional techniques to the circuit of thepresent invention as shown in FIG. l, for example by interchanging the Xand Y outputs of the resolvers 16 and -17 to the respective sweepampliiiers for both tubes 11 and 12, i.e., the Y output of resolver 16would be connected to the X ampliiier for tube 11, and the X and Youtputs of resolver 17 would be connected to the Y and Xamplifiers-respectively for tube 12, or by mechanically or electricallyrotating both sets of coils simultaneously. In practice, this may beaccomplished by reversing the resolver leads by, a suitable switchingarrangement. With such leads interchanged, the tube indications thatappeared in FIG. 4 now appear in FIG. 2 and the range marker lines 13.are spread suiciently to prevent them from moving pro= gressively closertogether, or from being superimposed one on the other.

Additional air targets A2 and A3 are shown developed in FIGS. 4 and 5,where the sweep has progressed through an additional 45 degree angle ineach view. In FIG. 6 the sweep of the degree sector has been completedwith the additional development of a sea target, such as a ship S1, andan additional land target or island, L2.

Some ambiguity also exists with respect to the targets A3 and S1 whichmight be resolved by a close observation of the timing as the sweepprogresses, but if desired, this ambiguity could also be readilyresolved by rotation of the field through a 90 degree angle in eitherdirection;

The present arrangement permits the resolutionof cer.- tain ambiguitiesby timing with a large degree offacility, since the correlation betweenthe scopes is relatively easy by a mere vertical alignment which could,if desired, be facilitated by vertical lines extending across bothscopes, however, the range markers serve substantially the same purposeand in most cases will provide suiiicient correlation between thetargets on the displays in the upper tube and the lower tube whichcorrespond to anV elevation and plan view in conventionalv drafting`techniques.

While the visual etect is diicult to portray in-a series of drawings,the correlation of targets is materiallyy assisted by watching the sweeponyboth tubes simultaneously with the same target showing on both theupper and lower scopes simultaneously and in direct vertical` sperrigealignment which facilitates the qualitative interpretation of thepicture as the sweep progresses.

If desired, the observation may be limited to a particular area on alarger scale by range expansion and range and sector gating, but stillmaintaining the correlation and vertical alignment oftargetsrtrnpresentrmrmrtorialmnmrnerelyingoiarethegproner;dengyolfthecireuits fai-grise representation which isreadily accepted and interpreted by the operator. Y

6 range for clear denition on the plan or X-Y scope 1i would be somewhatless. It will be apparent that cathode ray tubes withreitherelectro-magnetic or electro-static deection can bek uti-` lized inconjunction with the present invention and would therewith.

It is sometimes desirable particularly with raw'd-ata to It will beapparent that all three dimensions arrprr-rr maintain a sweep patternon'the'tubeswhich'correspons sented accurately to scale in the twoviews, the height being obtained accurately from the elevation view, andthe range and bearing, or if desired the X and Y coordinates, obtainedfrom the plan view on the lower tube.

In the vertical scan as showniromJlGnl. gg- ,while rhapgggr.gygtgmypagnghetagrarsgggr the range is such that the earths curvaturemust be considered and corrective adjustments made. Without adjustrnentthe uniform height reference line 14 would have to be curved upwardly inthe middle to follow the earths curvature contour and would furthercomplicate the reading of elevation. To bring all objects of the sameheight into horizontal alignment on the scope (making line 14horizontal'as shown), earth curvature corrections must be made to the Zor height dellection. Thus, by adding the earth curvature correctionvoltage to the Z-sweep voltage, the line between objects of the sameheight will be a straight horizontal line instead of a line curved inconformance with the earths surface.

The preferred means of automatically correcting target height data forearth curvature to provide accurate readout of height information isillustrated in FIG. 1, wherein an earth curvature correction voltagegenerator is con nected to the sync generator` and supplies a non-lineartime varying voltage having an amplitude proportional to the square ofthe instantaneous radar range which is added to a linear saw toothvoltage in the height sweep generator. The composite signal is modulatedby the trigonometric functions of the potentiometer on the elevationantenna to provide a non-linear Z-sweep voltage which combined asresultant forces with the linear X-sweep voltage produces upwardlycurving sweep traces on the XZ display in the upper tube 11. Thereforetarget lines of constant height above the curved surface of the earthsuch as line 14 would appear as straight horizontal lines on the XZdisplay and all targets could be directly interpreted with regard toheight and an accurate readout of height information could be obtainedregardless of range and bearing.

Y ,A joystick readout with or without tracking may also be utilized inconjunction with both the upper and lower tubes 11 and 12, followingconventional techniques.

It will be obvious that the circuit shown in block diagram form in FIG.1 which is adapted to accept the spherical input of raw radar can bereadily Vadapted to accept cylindrical data from raw radar or otheranalogous search and object locating systems such as sonar, or therectangular coordinates from synthetic data as supplied by a radar orsonar simulator.

While the system shown is adapted for use with a beam of energyconsisting of electro-magnetic radio waves, it will be obvious thatsimilar apparatus may be utilized with a beam of sound energy such asthat used in sonar or any other type of energy which may be convertedinto an electrical signal to supply video information to the cathode raytube or any other type of display device functioning in an analogousmanner...

The system shown in the block utilizes two antennas for practicalreasons, since the resolution'of the picture on the lower scope with theazimuthl antenna radiating a separate beam of energy in a single planeis much better than that which could be obtained with the scan of theelevation antenna lat a different pulse repetition frequency and noddingconcurrently with its rotational movement about a vertical axis.However, the X, Y and Z components or signals could obviously be alltaken from the elevation antenna utilizing only one resolver, but thepicture would not be as distinct and the raglan of HG to the antennamovement, however, using the present system in connection with syntheticdata on a trainer or simulator equipment, it is not necessary to providesweep of this nature. l

which covers 360 or complete area coverage with limited elevationalangle, it will be obvious that the sweep could cover a spherical orhemispherical volume or be restricted to a pyramidal volume for -use inconjunction with an aircraft landing system or for section iire controlwith the antenna nodding in a substantially vertical plane andoscillating between limits in a substantially horizontal` plane in whichcase the sweep on the scope would correspond to theantenna movement. Itmight even be desirable under certain conditions to search and displayin planes which are not perpendicular to each other. While both of thecathode ray tubes have been shown as circular, it will be yapparent thateither or both might be rectangular in shape and it may be desirable inorder to limit the space requirements of the design to provide arectangular tube for the X-Z display and a circular tube-for the X--Ydisplay. Another pair of tubes on the same circuit or an additional tubefor the display of the X-Z coordinates might be added to the presentcircuitry to provide both a front and side elevational view to eliminatethe necessity for rotation of the target field or to provide separatemonitoring of two or more separate sectors for tire control purposes. AA single tube could be utilized to display both XY and XZ views for a180 sector by time sharing the user of a common electron gunfstructureand deflection system.

Another preferred means of displaying both XYand XZ views on a singlescreen is the use of a single dual-gun electrostatic deflection type ofcathode ray tube as disclosed in the co-pending application of JohnDonahue for Three Coordinate Orthographie Displayk System, Ser. No.541,868, tiled October 20, 1955, now U.S. Patent No. 2,951,244, issuedAugust 30, 1960. Y

Other renernents which can be readily utilized in conjunction with thesystem and circuitry of the present invention as shown is the use ofpolar oli-centering, gating inrbearin'g and bearing sector, gating inrange and range sector, or gating in both bearing and rangesimultaneously by separate controls, and an area coverage indicator toShow the portion of the maximum area covered by the search system whichis displayed on the XZ and XY tubes when using expanded scales andgating. Conductive glass overlay for readout of coordinate informationmay also be utilized readily in conjunction with the paresent system toprovide a rapid indication ofthe position coordinates of all targetswith respect to any desired origin. i

Automatic tracking and plotting can also be adapted readily to thesystem and apparatus of the present in-` vention, and results can bereadily interpreted without for use with photographic techniques, wherea series of pictures may be taken of both tubes simultaneously andreadily interpreted to follow the progress of any action or activity ina particular area at a later time.

'Ihe circuit shown in FIG. 1 may also be modified and with a simpleswitching arrangement can selectively display an isometric view in theupper tube 11. Such an arrangement is disclosed in the tro-pendingapplication of L. G. Harris, Ser. No. 385,900, tiled October 13, 1953.

Obviously many modifications and variations of the.

F7 l' present invention are possible in the light of the aboveteachings. It is therefore to be understood that within the scope of theappended Yclaims the invention may be practiced otherwise than asspecically described.

What is claimed is: y

1. A three coordinate radar display system comprising a pair ofvertically aligned cathode ray tubes each having an indicating electronIbeam with detiecting elements and an intensi-ty control operative tocontrol said indicating beam', an antenna system adapted to scan avolume of space with a narrow directional beam of energy, said antennaSystem being rotatable `about a substantially vertical axis andoscillatable about a substantially horizontal axis, a sweep generatoradaptedl to generate a sweep voltage, means operatively connected tosaid sweep generator and actuated by rotation of said antenna systemabout' said vertical axis for generating X and Y sweep voltagesproportional to `the rectangular coordinates corresponding to theAangular position of said antenna system about said vertical axis, aheight sweep generator, a potentiometer associated with said antennasystem and adapted to generate a voltage proportional to the angularposition of said antenna about said horizontal axis, said potentiometerbeing operably associated with said height sweep generator to provide aZ sweep voltageV proportional to the angular position of said antennasystem about said horizontal axis, means for' applying the X and Z sweepvoltages to the deilecting elements of the upper one of said cathode raytubes, means for applying the X and Y sweep voltages to the deliectingelements of the lower one of said cathode ray tubes, and means fortransmitting andjreceiving a yseries of' radio-frequency pulses throughsaidantenna system and applying the echo pulse signal from an object insaid volume of space to the intensity controls of said cathode ray tubesto produce a visible display on said tubesY representing the objects insaid volume by spatial coordinates in three dimensions with the* commoncoordinate display in alignment on both of saidtubes.

2. three coordinate radar display system comprising a pair o fvertically aligned' cathode ray tubes each having anV indicatingelectron beam with deiiecting coils and anint'ensity control gridoperative to control said indicating beam, an antenna system adapted toscan a volume of space with a'narrow directional beam of energy, saidantenna system being rotatable about a substantially vertical axis at arelatively low angular'velocity and oscillatable` about' a substantiallyhorizontal axis at a relative- Iy'high angular velocity, a sweepgenerator adapted to generate a sweep voltage, a resolver operativelyconnected to said sweep generator and actuated by`rotation` of saidantenna system` about said veritical axis` for generating X4 and Y sweepvoltages proportional to the rectangular coordinates-corresponding tothe angular position of said antenna system about said vertical axis, aheight sweep generator, .aV potentiometer associated with said antennasystem and adapted to'generate a voltage proportional to the angularpositionoi'saidl antenna about said-horizontal- Iaxis,` saidpotentiometer' being, operably associated with said height sweepgenerator to provide a Z sweep voltage proportionalto theangularposition'of said' antenna'system about saidfltorizontal axis, means forapplyingiftliel X -and'Zsw'eep voltages to thedeecting coils ofi therupperone'of-saidcathode ray tubes, means for' applyin-'gthefX andfY'sweep volta-gesl to the detlecting coils ofi the lower one of. saidcathode ray tubes, and means fortrans'mitting and receiving a's'erie'sor" radiofrequency pulse-s through'saidantenna systemand'applyingfthef'echo pulse' sign-'al from any object in 'said Volumeof spaceto the' intensity controls of saidy cathode ray tirbesto producea4 visible display on' said `tubes representing tire; objects inA said4volume by spatial rectangular coordinates-inthiee dimensions with thecommon X, co'- ordinate displayed la'alignment on beth of'said'tubesl 3.A three coordinatelradar display system comprising a pair ot displaytubes eaeh having an indicating Vbeam with deecting elements and anintensity control operative to xirit'rolv said indicating beam, anantenna system adapted t'o scan a volume of space with a narrowdirectional beam of energy, said antenna system being adapted to varythe direction of said beam of energyV about a substantially verticalaxis and about asubstantially h orizontal axis, a sweep generatoradapted to generate a sweep voltage, means" operatively connected tosaid sweep-r generator for generating X land Y sweep voltagesvproportional to the rectangular coordinates corresponding to theangular position of said beam of energy about'said vertical axis, aheight sweep generator adapted to provide alinear .saw-tooth voltage,selectively operable means associated with said height sweep generatorto add a nonlinear earth curvature `correction voltage to said linearvoltage, means operably yassociated with said height sweep genenator toprovide a' Z sweep voltage related to' the angular position of said beamof energy about said horizo'ntal axis, means for' applying the X and Zsweep voltages to the deflecting elements of the upper one of saidcathode ray tubes, means for applying the X and Y sweep voltages -to thedeliecting elements of the lower one of said cathode ray' tubes, andmeans for transmitting and :receivinga series of radio-tirequency pulsesthrough said antenna syste-m and applying the echo pulse sign-al froma'n object' in said volume of space to the intensity controls of saidcathode ray tubes to produce a visible display on said tubesrepresenting the object in said volume byV spatial coordinates in threedimensions with the commoncoordinate displayed in alignment on both ofsaid tubes; v

4'. `In a direction, ranging and elevation system, in combination, anantenna rotatable in azimuth and oscillatable in elevation, a cathoderay tube having beam defleeting means, means forobtaining a iirst sweepvoltage having an amplitude proportional to the trigonometrical functionof the azimuth angle of said antenna, means for applyingsaid voltage tosaid rst deecting means to dellecttle beam inV a horizontal direction onthe screen of said tube,r means for obtaining a second sweep voltagehavingan amplitude proportional tothe elevation angle of said antenna,means-for applying said second voltage -to said dellecting means todeiiect the beam in a vertical direction on the screen of said tube,means for synchronouslyredueingboth said voltages to zero intermittentlyatvapedeterminedffrequency, the trace of said beam in response todeflection'by said voltages simulating the appearance on said 'tubescreen of a triangular are'a'indicative of? the? elevation sweep of saidantenna, said triangular area rotatable-in vsynchronization with theazimuth sweep of'saidantenna abouta vertical axispassing through thezerodefl'ection position of said beam topresent oblique projections otgsaid triangular area at all azimuth positions except and 180 azimuth.

5. Thesystem of claim 4, including a second cathode ray. tube havingbeam deiiecting means, means forl obtaining a voltage identical withsaid first mentionedY voltage; means `for obtaining a second voltage inquadrature phase relationship with said rst voltage proportional toanother trigonometrical function of the azimuth angleof said antenna,means for applying both said last mentioned voltages to said deflectingmeans to produce a` plan position indication type of beam deliection onsaid second tube screen, and means for synchronously reducing thevoltages of Aasid second tube -to zero intermittently at saidprecleterr'n'inedV frequency.

6'. The'system of claim 5, including' means'for indicating horizontalrangey on both tubes, said rangey indicating rn'ean's` in" both tubesbeing in alignment throughout Aa complete" azimuth sweep.

(References on following page) References Cited in the le of this patentUNITED STATES PATENTS Fyler Sept. 23, 1947 Ayres Aug. 31, 1948 Wolff eta1. Ian. 18, 1949 Lee Jan. 29, 1952 Sherwin et al. Feb. I12, 1952 FylerOct. 28, '1952 10 2,637,025 Cutler Apr. 28, 1953 2,649,581 Tasker et a1.Aug. 28, 1953 2,663,868 Tasker Dec. 22, 1953

